Photodynamic Therapy (PDT) relies on accumulation of an inactive photosensitizer (PS) drug in the tissue of interest followed by local illumination at the appropriate wavelength. The excited PS reacts in situ with molecular oxygen to produce highly cytotoxic reactive oxygen species (ROS) that lead to necrosis of the treated tissue. PDT represents a relatively new approach to cancer therapy such as lung, stomach, bladder, cervical, esophageal and skin cancers (Sibata et al., 2001; Hopper, 2000) and therapy of non-malignant diseases, e.g. alopecia, psoriasis, mesothelioma and menorrhagia (Dougherty, 2002), as well as in cardiology, for example in restenosis after angioplasty or atherosclerosis (Mansfield et al., 2001). and ophthalmologic diseases such as age-related macular degeneration (Fine, 1999).
A novel family of PSs derived from the photosynthetic pigments chlorophyll (Chl) and bacteriochlorophyll (Bchl), particularly from bacteriochlorophyll a (Bchla), has been recently synthesized in the laboratories of the present inventors for use in PDT, diagnostics and killing of cells or infectious agents in vitro upon illumination (Zilberstein et al., 2001; Rosenbach-Belkin et al, 1996; Gross et al., 1997; Schreiber et al., 2002; Koudinova et al 2003; U.S. Pat. No. 5,726,169; U.S. Pat. No. 5,955,585; U.S. Pat. No. 6,147,195; EP 0584552; WO 97/19081; WO 00/33833; WO 01/40232; and Israeli Patent Application No. 152900).
The lead compound from the novel family of PSs developed by the inventors, Pd-bacteriopheophorbide (Pd-Bpheid) (Schreiber et al., 2002; WO 00/33833), exhibits superior photochemical and pharmacological characteristics over clinically used PSs. Pd-Bpheid exhibits higher phototoxicity and photostability, faster clearance rates from the circulation with little or no damage to adjacent tissues, and strong absorption in the near infrared (760 nm) with Σ0˜105, enabling deeper photosensitization into the tumor tissue ˜1.5 cm. Pd-Bpheid (Tookad®, Steba Biotech Ltd.) was tested in preclinical PDT treatment of normal canine prostate and shown to cause full necrosis of the tumor without functional urethral damage or damage to other adjacent tissues (Chen et al., 2002). Pd-Bpheid is now in advanced clinical trials for PDT of human prostate cancer.
Illumination of a tumor treated with bacteriochlorophyll-serine (Bchl-Ser), a PS described in EP 0584552, was shown by the present inventors to lead to light-dependent oxygen depletion (due to O2 photoconsumption) (Zilberstein et al., 1997). Instant illumination following intravenous sensitizer administration (with no drug-light time interval (DLTI)) was shown to induce capillary occlusion, hemorrhage and blood stasis, resulting in tumor necrosis and eradication (Zilberstein et al., 2001). This novel anti-vascular treatment modality with Bchl-Ser or Pd-Bpheid was shown to induce high cure rates for melanoma, glioma, sarcoma and human prostate xenografts in mice (Zilberstein et al., 2001; Schreiber et al., 2002; Koudinova et al., 2003) and rats (Kelleher et al., 1999). PDT with Pd-Bpheid also decreased the incidence of metastasis, compared with conventional surgery (Schreiber et al., 2002). In studies performed with other sensitizers such as the chlorin-based photosensitizer MV6401 and the benzoporphyrin derivative verteporfin, similar hemodynamic alterations were related to short or no DLTI (Dolmans et al., 2002; Fingar et al., 1999; Pogue et al., 2001).
Precise light delivery is a prerequisite for accurate, efficient and safe PDT. While fiber insertion into internal organs can be assisted by various techniques such as optical, X-ray or ultrasound, real-time visualization of the light impact and tumor response is presently unavailable. The need for such a technique becomes critical in cases where the target tumor is internal, and/or located in the proximity of vital organs, nerves or major blood vessels. In such cases, it would be of advantage to enable imaging of the photosensitized treatment zone. Therefore, such an imaging technique will potentially enable higher treatment accuracy and safety, thus decreasing unwanted damage to neighboring non-diseased tissues.
Magnetic resonance imaging (MRI) can define human anatomy at a level of detail that cannot be achieved by any other medical imaging technique. In addition to depicting anatomy, MRI can evaluate tissue function. Recently, functional magnetic resonance imaging (fMRI) was developed as a technique for analysis of brain function (Detre and Floyd, 2001). fMRI enables detection and imaging of spatial and temporal changes in blood oxygenation, flow, and volume (Jordan et al., 2002) and includes blood oxygen level-dependent (BOLD) imaging, diffusion imaging, perfusion imaging, cerebrospinal fluid flow analysis and MR spectroscopy.
BOLD-MRI is an imaging protocol that is sensitive to specific relaxation rates which are influenced by deoxyhemoglobin. BOLD-MRI contrast is derived from the inherent paramagnetic contrast of deoxyhemoglobin using T2* weighted images (Howe et al., 2001; Turner, 1997). BOLD-MRI contrast was applied previously in cancer research for monitoring tumor response to vasomodulators (Jordan et al., 2000; Taylor et al., 2001), and by the present inventors for analysis of tumor vessel functionality, vessel maturation, and angiogenesis (Abramovitch et al., 1998 a, 1998b; Gilead and Neeman, 1999).